why AC(alternating current) cant be stored ,like DC in batteries ?

The AC(alternating current) is the current or voltage whose magnitude (generally 230V in India and 100V in US) varies with time with some frequency (generally 50Hzs in India and 60Hzs in US) , but in the case of DC the magnitude of the is constant with time (like a step function).so DC has no frequency. 

       
                          

                                       DC-Voltage

we can see from the above pictures that the AC varies with time but DC is constant, moreover the DC voltage has a average value, but the average value of the AC voltage is zero for full cycle.The capacitor can store only DC voltage because average value is equal to the dc voltage,but in the case of the AC voltage,we  cant store because it average value is equal to zero.

      Here we are considering the case of capacitor only because all the practical batteries are nothing but capacitors which can with stand based on their voltage ranges. 

# So for this reason we are interested in storing in DC voltages only